Theres a wiring diagram here m8

http://www.xrweb.co.uk/code/fuel.htm

The extra bits you need are the fuel flow sensor and the speed sensor, speed sensors ok as all MFI with the computer and all post 90 EFI cars are fitted with one it goes on the top of your gearbox where the speedo cable goes in between the speedo cable and gearbox, the fuel flow sensor is harder to get hold of as only the MFI cars with the computer fitted as an option have them (the EFI cars use an output from the ECU) the sensor fits on the side of the metering head.
The wiring to the fuel sender is already there under the back seat.
You can fit the fuel computer and wire it up without the speed and fuel flow sensors with just the fuel level sender wired up, this will give you your 'range' function but based on a default of about 25 mpg, it still looks better than the coin tray!

HTH
Steve